Crystal Growth & Design最新文献

Hybrid organic–inorganic perovskite (HOIP) crystals are promising optoelectronic materials, but little is known about either the thermodynamic and kinetic controls on crystal growth or the underlying growth mechanism(s). Herein, we use fluid-cell atomic force microscopy (AFM) and solution nuclear magnetic resonance (NMR) spectroscopy to investigate the growth of the model HOIP crystal CH₃NH₃PbBr₃ (MAPbBr₃) and to determine how formic acid (HCOOH) modulates the thermodynamics and kinetics of growth. The results show that growth of MAPbBr₃ in dimethylformamide (DMF) proceeds through the classical pathway by the spreading of molecular crystal steps generated at screw dislocations on the {100} surface. Temperature-dependent step velocity measurements demonstrate that with increasing concentration, HCOOH decreases the solubility of MAPbBr₃. From the AFM data, we also determine the apparent kinetic coefficient (β) of step movement as a function of HCOOH concentration. ¹H NMR measurements indicate that HCOOH increases the lifetime of the methylammonium (MA⁺) ions and promotes the association of MAPbBr₃, thus tuning the solubility of the perovskite. We further propose that HCOOH alters the molecular tumbling motion and bulk diffusion of the MA⁺ ions, possibly via H-bonding. Our findings establish a direct correlation between the mesoscale crystal growth kinetics and the molecular-scale interactions between organic additives and constituent ions, providing unprecedented insights for developing predictive syntheses of HOIP crystals with defined size, crystal habit and shape, and defect distribution.

The interactions among monomers in an expanded π-conjugated group directly influence the geometry and, consequently, the macroscopic performance of the resulting crystalline material. Therefore, investigating the interaction mechanisms that impact the geometry of the expanded π-conjugated group is a crucial issue. Herein, we report three bridged-bipyridine halides (2,2′-dipyridylamine, 2,2′-dipyridylsulfonamide), denoted as (C₅H₄N)NH(C₅H₄NH)Cl·2H₂O (1, Cc), (C₅H₄N)NH(C₅H₄NH)Br·2H₂O (2, Cc), and (C₅H₄NH)₂SBr₂ (3, I4₁cd), to demonstrate the influence of intramolecular hydrogen bonds (HBs) on controlling the coplanarity of the two linked pyridine rings, thus impacting the macroscopic optical isotropy. Single crystal diffraction data reveal that the presence of different bridging atoms (S in 3 vs N in 1 and 2) led to distinct dihedral angles of 64.4 versus 2.1 and 1.8°, respectively. Experimental studies indicate that while compounds 1–3 all exhibit moderately strong second harmonic generation (0.32–1.1 × KDP), their birefringence (Δn) varies significantly. Compound 3 has a very small (Δn_cal.; _obv.) value of (0.03_cal.; 0.048_obv.), whereas 1 and 2 have values 1 order of magnitude larger (0.26_cal.; 0.25_obv.)/1 and (0.30_cal.; 0.28_obv.)/2, at 550 nm. In-depth analyses demonstrate that this difference is attributed to the nearly coplanar alignment of the bridged-pyridine rings in 1 and 2, which is achieved by the intramolecular HBs that restrict the rotation of the N–C single bond.

Rare-earth (RE)-doped transparent tellurite glass-ceramics (GCs) embedded with “anti-glass” crystallites not only exhibit superior emission properties but can also be a potential medium for nonlinear optical (NLO) applications. Both of these properties depend on their transparency. Keeping this in view, we aimed to elucidate the effect of Nd³⁺ ion concentration (0.5–2 mol %) on the crystallization mechanism of lanthanum-gadolinium-titanium-tellurite (LGTT) glass in retaining the transparency and NLO properties. XRD reveals the precipitation of (La/Nd)₂T₆O₁₅ and Gd₂Te₆O₁₅ “anti-glass” crystallites upon ceramization of these glasses. Particle-size-dependent DSC confirms competition between the growth of these two crystalline phases at higher Nd³⁺ concentration that aids in controlling crystal growth. The FE-SEM microstructures demonstrate a change in morphology of the crystallites from rectangular (1.5 μm) to spherical (120 nm) with increasing Nd₂O₃ concentration from 0.5 to 2 mol % and thereby retaining optical transparency (12% → 55%) in GCs. Photoluminescence spectra reveal a maximum emission intensity for 1 mol % of Nd₂O₃-doped glass; however, the lifetime is maximum (156 μs) for 0.5% Nd₂O₃ doping. This study also discloses an enhancement of third-order NLO properties as a function of Nd₂O₃ concentration in LGTT glasses under femtosecond laser excitation at 800–1200 nm due to resonant nonlinearity. Emission intensity and NLO responses are increased in the GCs compared to their parent glasses. A maximum nonlinear absorption coefficient (α₂) of 4.986 × 10^–10 m/W and nonlinear refractive index (n₂) of 3.115× 10^–17 m²/W has been obtained from LGTT-Nd2(GC-36h) GCs at 800 nm. GCs exhibits an optical limiting threshold of 4.14 mJ/cm², suggesting its great potential for intense radiation shielding.

The discovery of superelastic organic crystals capable of phototwisting and photobending represents a significant advance in the field of light-responsive materials. This research focused on the synthesis and characterization of crystals derived from trifluoromethyl-substituted acylhydrazone derivatives, known as TBMP. These crystals exhibited remarkable superelasticity when subjected to mechanical forces along their (010) crystallographic plane while showing a tendency to fracture along the (001) plane. Single-crystal analysis revealed that hydrogen bonds, especially C–H···F, C–H···O, and C–H···N interactions, are crucial in providing the crystals with superelastic properties. In addition, reversible E ↔ Z isomerization of TBMP molecules occurred under UV irradiation and heating, resulting in photomechanical (twisting or bending) and thermal recovery behavior of the crystals. Due to their exceptional properties, these crystals possess significant potential for application in robotic arm technology.

Helix structure is a very important and fundamental structural feature of DNA and other biomaterials and is also one of the origins of chirality. Diversiform helix structures have been designed and constructed to understand the mechanism of helix formation. One of the challenges in this field is rationalizing single-stranded DNA and water helix. The possibility of water helix formation preceding the base pairing in DNA is an intriguing prospect. In this work, three coordination polymers based on the nucleotide dTMP have been designed and studied. Their single-crystal structures revealed that complexes 1 and 3 are 1D coordination polymers while complex 2 is a 2D coordination polymer. Complexes 1 and 2 are the coordination helixes. Importantly, the water helixes are enclosed in them. Both P and M water helixes exist in complex 1; only the M-water helix is in complex 2. It is worth noting that complex 3 exhibits the entanglement of coordination helixes and water helixes and then presents a pseudowater helix. The solidarity of the coordination helix and water helix in the crystal lattice has been investigated based on crystallography analysis. The building synthons limit the orientation of the nucleobase and lack adequate stereospace to confine the guest water molecules. A new type of nucleobase pairing, thymine–thymine, named T-motif, has been observed for the first time. The inherent and supramolecular chirality of these complexes have been discussed according to CD spectra in both solution and crystallized solid states. The water helix in complex 2 exhibits characteristic outcomes in the CD spectrum. The research results contribute to exploring and understanding the DNA structure and properties and the mechanism of helix formation.

Caffeine shares many qualities with drugs and biomolecules and is an ideal model to explore the effectiveness of available crystal structure analysis tools for cocrystal structure comparison and design. Two new cocrystal structures of caffeine and phenylboronic acid are reported; these arrangements are compared with each other and the broader crystallographic literature for hydrogen bonding, aromatic interactions, and predicted and measured crystal morphology.

This research uses caffeine cocrystals to showcase modern crystal structure analysis tools and highlight best practices in cocrystal polymorphism studies.

Two-dimensional (2D) tetragonal FeTe is expected to show attractive properties in different fields. However, the synthesis of high-quality 2D tetragonal FeTe via a facile approach remains challenging. Herein, we propose a facile chemical vapor deposition (CVD) strategy to realize the preparation of ultrathin tetragonal FeTe flakes on a Au foil substrate. The tetragonal FeTe flakes are as thin as 3.9 nm and have a high crystalline quality. The as-grown 2D tetragonal FeTe is shown to be a wonderful hydrogen evolution reaction (HER) catalyst with good activity and stability. This research injects new vitality into synthesizing 2D tetragonal FeTe for electrocatalytic HER applications.

Unequivocally establishing chemical connectivity and ultimately chemical identity is of central importance to all branches of science and particularly chemistry. Accordingly, the determination of a crystal structure is often considered the “gold standard” as this technique can unambiguously establish both the connectivity and identity of a compound. Crystal structure data, however, are prone to misinterpretation, and the increasing development of automatic data processing and verification has the potential to result in an epidemic of incorrectly modeled crystal structures. Here, we present a series of case studies where structures were modeled to current publication standards with the incorrect chemical composition. It is essential that researchers, referees, editors, and the scientific community be vigilant in upholding the scientific method.

Copper-based halide perovskites are evolving as alternative materials to lead-based perovskites. Herein, we report the synthesis of double organic cation copper-halide perovskites (C₄H₉NH₃)_x(3-BrC₃H₆NH₃)_2–xCuCl_2+xBr_2–x (x = 0.7, 1.0, 1.3, 1.6, and 1.9). The crystal structures were studied by powder X-ray diffraction (XRD). The optical properties of the perovskite thin films were investigated by UV–vis absorption spectroscopy and spectroscopic ellipsometry. It was demonstrated that the use of multiple cations is an effective compositional strategy to control the structural properties of two-dimensional (2D) perovskites. In addition, the thermochromism was also investigated by differential scanning calorimetry and in situ temperature-dependent powder XRD. This topic opens up a path for 2D copper-based halide perovskites to adjust their optical properties via spacer cation engineering. This research inspires future research interests in designing environmentally friendly 2D metal halide perovskites.